Maritime shipping is the lifeblood of international trade, and it’s all thanks to the modern container ship. These floating skyscrapers can carry as many as 15,000 containers 20-ft. long containers, enough to carry 745 million bananas—one for every European and North America. (I took that fact from Rose George’s upcoming book Ninety Percent of Everything, which looks fabulous.) Container ships—which can unload and load their cargo via those regularized container far quicker than ships in the past—carry everything you can buy, and their existence is what enables the cheap flow of goods from the developing world to the developed one. Without container ships, you really would have to buy American.

But shipping incurs an environmental cost. According to the International Maritime Organization, sea shipping accounts for around 3 to 4% of global CO2 emissions. That may not sound like a lot—and because container ships can carry so much, they’re relatively efficient on a ton per mile basis—but as shipping industry grows, so does its carbon footprint. And the local pollution produced by container ships as they steam in and out of port can be severe because they usually burn low-grade ship bunker fuel that is painfully high in polluting sulphur. In 2009 it was calculated that the largest 15 ships could be emitting as much carbon and greenhouse gases as 760 million cars.

So the maritime shipping industry could stand to go on a carbon diet. Some of the big players, like Denmark’s Maersk, have already made moves to improve environmental performance—its massive Triple-E container shops will be able to hold more cargo, requiring fewer trips, while its more efficient engines and waste heat recovery system could help cut the cost of long-distance transport. Just this past week, the first Triple-E—which will hold 18,000 20. ft containers, the most in the world—just set off on its maiden voyage from the Port of Tanjung Pelepas in Malaysia. The company believes the Triple-E will be able to cut carbon emissions per container moved in half.

But efficiency can only get you so far—as maritime companies reduce fuel costs, they’ll be able to use some of those savings to increase shipping, cutting into the carbon reductions. (This is known as the “rebound effect,” though researchers disagree on how large it might be for maritime shipping.) Truly green shipping would require crafts that don’t depend on fossil fuels, like the sail-powered hybrid container ship being designed by the Dutch company Dykstra, or even solar-powered cargo ships. What would a greener era of martime shipping be like? TIME contributor Laurent Laughlin has the above video report.